Cell division and multiplication

Transcription

1 CELL DIVISION

2 Cell division and multiplication As we already mentioned, the genetic information contained in the nucleus is hereditary Meaning it is passed on from cell to cell; from parent to child This happens during cellular reproduction

3 Cell division and multiplication Why would cells need to reproduce? To increase the number of cell (in other words, to grow) To repair damaged tissues To produce gametes (sex cells)

4 Cellular Reproduction To reproduce a whole individual, humans require sexual reproduction And this requires the product of sex cells (gametes) through meiosis But we do sometimes need to reproduce individual cells for growth or repair through asexual reproduction And this is done through mitosis

5 Mitosis vs Meiosis There are 2 types of cellular reproduction: Mitosis: when a cell divides to produce 2 identical daughter cells Used for growth and repair in somatic cells Meiosis: when a cell divides to produce 4 reproductive cells that are each different from the original cell. These daughter cells only contain half the genetic material of the parent cell Used to create gametes (sex cells)

6 Mitosis Ensures growth (an increase in the number of cells that make up an organism). When our bodies grow so does the number of cells, so we have more cells when we are adults than when we were babies Mitotic activity: number of mitoses carried out by cells (more intense during childhood and adolescence than any other stage of life) How often the cells undergo mitosis

7 Mitosis Ensures repair of damaged tissues (ex. injuries, cuts, fractures, etc) or tissues that have become worn out Certain cells wear down more easily than others and need replacing more often E.g. skin cells are replaced every 2 weeks and white blood cells every 120 days)

8 Mitosis

9 Steps of Mitosis 1. DNA unravels 2. DNA duplicates 3. DNA condenses into chromosomes 4. Chromosome pairs split Half go to one end, the other half to the other 5. New nuclear membrane forms around the two new cells Go from 1 diploid cell to 2 diploid cells

10 Diploid vs Haploid Diploid: A cell that contains 2 complete sets of chromosomes (one from each parent) 2n Haploid: A cell that only contains 1 complete set of chromosomes (half of what is needed to make a full individual) n

11 Mitosis 2n 2n 2n

12 Meiosis Meiosis is a form of cell division that produces 4 reproductive cells that are different from the original cell because they each contain half the DNA The result is 4 daughter cells, each contain 23 chromosomes and all different genetic material. Each daughter cell ends up with half the genetic info. These are called haploid (n) cells. This is used to create sex cells Sex Cells: sperm and ova (eggs), are also called gametes

13 Meiosis 2n 2n n

14 Meiosis In order to produce cells that contain only half the DNA, there are TWO divisions that take place. The first one is similar to mitosis (where DNA doubles itself first) The second division happens right after the first division, but without duplicating the DNA

15 Steps of Meiosis 1. DNA unravels 2. DNA duplicates Go from 1 diploid cell to 4 haploid cells These are the gametes (sperm or ova) 3. DNA condenses into chromosomes 4. Homologous chromosomes pair up and swap sections of DNA 5. Cell splits into two diploid cells with homologous pairs 6. Each of these cells then splits again 7. Nuclear membrane forms

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18 MITOSIS & MEIOSIS ACTIVITY

19 Why is it important that sex cells only have ½ the number of chromosomes?

20 Meiosis and Fertilization Meiosis prevents DNA from doubling with every generation. During fertilization millions of spermatozoa (n) encounter the ovum (n). Only one sperm will be able to penetrate the ovum and combine the male genetic info (n) with that of the female (n) to produce a zygote (2n). From there, mitosis results in the development of an embryo (the first steps to a baby)

21 From there, the zygote will undergo many repetitions of mitosis in order to grow!

22 Cellular Organization Remember: 23 pairs give a total of 46 chromosomes of which ½ come from the mother and ½ from the father. 22 of the 23 pairs are similar in both sexes The 23 rd pair is made up of the sex chromosomes A chart showing the pairs of chromosomes in descending order of size is called a karyotype

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24 Karyotype of a male Karyotype of a female

25 Why is it important that sex cells are NOT identical to the parent cell?

26 Genetic Diversity Genetic diversity: is the variation of genes among the individuals of the same species. Prevents extinction of a species Ex: not all susceptible to the same diseases, etc

27 Factors that Contribute to Genetic Diversity Genetic recombination: similar chromosomes exchange parts of their genes during the beginning of meiosis Genetic mutation: where random changes happen in the bases of DNA (A,C,T,G). This can be caused by UV rays, X rays or cigarette smoke. Population mixing: where individuals from different populations breed

28 What comes next? Single-celled organisms can perform all the basic functions to survive. Multi-celled organisms being more complex require cells to specialize and work together to perform these same functions. These cells are grouped into: Tissues Organs Organ Systems Organism